Embolization treatment involves the introduction of a material into the vasculature in order to block the blood flow in a particular region. This procedure may be used to treat non-cancerous tumors, such as uterine fibroids, and cancerous tumors. Vascular occlusion in the case of tumors may be used to suppress pain, limit blood loss during surgery, or to cause tumor necrosis. In addition, embolization treatment may be used to control bleeding caused by conditions such as stomach ulcers, aneurysms, and injury. Treatment of arteriovenous malformation (AVM), where abnormal connections occur between arteries and veins, may also be through embolization to block blood flow.
Characteristics of the embolization treatment, such as ease of material delivery to the desired site and effectiveness of occlusion, are generally related to the properties of the material used in the treatment. Hydrogel microspheres have been used in embolization treatment. Characteristics of the embolization treatment are generally related to the properties of the specific type of hydrogel microspheres used in the treatment. The properties of the hydrogel microspheres are in turn generally dependent upon the materials used in microsphere preparation and the process by which the microspheres were prepared.
U.S. Pat. No. 6,218,440 discloses a process for preparing hydrogel microspheres which produces microspheres that have many cavities joined by interconnecting pores, with cavities at the interior of the material in communication with the surface. In the process disclosed therein, an emulsion is first prepared, and then this emulsion is suspended in an oil medium. The resulting microspheres have high absorption capacity and are said to be useful for adsorption of fluids or chemicals. These microspheres are not used in embolization treatment.
U.S. Pat. No. 4,446,261 discloses a process for making hydrogel microspheres which includes dispersing a solution containing monomer, crosslinking agent and initiator in a dispersion medium consisting of hydrocarbons having from 6 to 10 carbon atoms or halogenated aromatic hydrocarbons, with a protective colloid dissolved in this oil material.
U.S. Pat. No. 6,436,424 discloses microspheres suitable for dermal augmentation that are said to swell upon contacting physiological fluids at toe injection site to up to four times the average diameter of the microspheres prior to injection. These hydrogel microspheres are said to be made by standard methods of polymerization and microsphere preparation described in the art. The microspheres described in U.S. Pat. No. 6,790,456 are the same as those described in U.S. Pat. No. 6,436,424.
WO 2001072281 discloses hydrogel microspheres as described in U.S. Pat. No. 6,436,424 and U.S. Pat. No. 6,790,456 that are associated with bioactive therapeutic factors such as drugs, genes and diagnostic agents, for use in embolization.
JP1994056676A discloses a suspension used for embolization containing lipidic contrast agent and highly water absorbant hydrogel particles of vinyl alcohol and sodium acrylate polymer that are approximately 1.0 mm in diameter or less.
There remains a need for microspheres with novel and advantageous properties that when administered for embolic treatment provide durable blockage of blood flow at target sites.